Angiotensin I, composed of 10 amino acids, is produced through the action of renin, a proteolytic enzyme produced in the kidney, on angiotensinogen present in the serum. Angiotensin converting enzyme acts on angiotensin I releasing a dipeptide from the C-terminus to produce an octapeptide known as angiotensin II which has significant hypertensive activity. Angiotensin converting enzyme is also known to inactivate bradykinin, a substance having hypotensive activity. Accordingly, an angiotensin converting enzyme inhibitor is clinically effective for the prevention and treatment of hypertension.
Conventionally known native substances having angiotensin converting enzyme inhibitory activity include venom peptides and analogues thereof, peptides obtained by treating milk casein with trypsin, as described in JP-B-60-23085, JP-B-60-23086 and JP-B-6l-5l562 (the term "JP-B" as used herein means an "examined published Japanese patent application"), and peptides extracted from the tissue of fishes, as described in JP-A-1-313498 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") (corresponding to EP-A-345778). Further, it has been reported that an extract of lactic acid bacteria contains a substance having angiotensin converting enzyme inhibitory activity (Igaku to Seibutsugaku, Vol. 116, p. 159 (1988)). However, these known angiotensin converting enzyme inhibitors have disadvantages, such as a need for enzymatic treatment with, for example, trypsin, and difficulty in culturing microorganisms.